Center console speaker box questions - Page 3 - Ford F150 Forum

loganberry · 03-10-2010, 12:02 PM

Okay, some people will hate me for posting this, hopefully no one on the great world famous SMD forums :^ But I see alot of people asking about 1/4 wave T -line, Horn design/theory. All I ever see is people sending links, and thats all I ever did to, was send links- to confusing brain boggler websights. When honestly, 1/4 wave theory is easier than trying to calculate port dimension with no program. Anyone with simple 8th grade- no scratch that, 6th grade level math can calculate tline enclosure dimesnions.
Most websights say how Tlines are un-realistic for cars, yeah, a 15" with a 24hz Fs, is pretty unrealistic. But a 12" with a 40hz bass boost can be as small as a sql box, for the same subwoofer. 40hz quarter wavelength is only 7.06ft long (round to about 7ft) When 24hz is 11.77ft long, and then multiply that 11.77ft by the SD of the cone... Pretty damn big box Just 1 -15" tuned at 24hz will yeald about a 14+cf box. Maybe good for a large van, but definitley not a car.
Over the years I have learned tricks, and short cuts to tlines. I stick with tlines, because personally, its the Perfect box, for your sub. No more of that, "What box sounds best for my sub?" If you do a tline based on your subs Fs, That IS the perfect box POSSIBLE for that sub. Its in the environment that subwoofer is built for, with absolutley NO amplifier strain, yet huge db outputs. I still have never pwersonally ran over 500watts to a tline, yet I always stay in the low 140db-high 130s with awesome SQ. Another Main plus side to tlines are, there is no back presure to keep efficiency up, xmax up, and allows the subwoofer to stop on a dime, and start back up faster than sealed, or ported designs.
So, heres the formula, its simple, you would just need a pen , paper, and calculator. Quarter wave is all based on speed of sound, and length of the sound wave.
Sound travels at 1130ft / sec
to calculate length of Freq Devide 1130 / (freq) say 30hz
1130/ 30 = 37.66 ft long Full wave length But we need to devide this by 4- for 1/4 wave wich equals= 9.41ft long
Pretty long huh? And the worst part is, to have a true T-line, you need to keep the port/tunnel/line - a Line, that equals Cone area, or pretty close to it. If you have a 10" The average SD/Cone area is about 50-60sq inches (to find SD in inches, you measure the cone, by useing a tape measure, and measure from middle of surround, to middle of surround on opposite side) 10" is usually close to 9"- 8.5"-9". This is where Pie comes in 9"/2 = 4.5-------- 4.5"x 4.5"x 3.14" = 63.58sq"
That is your Port AREA ( usually round this number Down- say 60sq")
So, a Tline for a 10" with a Fs of 30hz, and a cone area of About 60sq inches, will be about 9.25ft-9.5ft long (rounded) Its okay to be a little off, because this is car audio tlines, the cars accoustics will not notice it, because of cabin gain. But, when building a t-line for a sub based on Fs, you need to keep in mind the speakers Qts, and Qms, they should be low for SQ, Qts of .40 and lower, and Qms of 7 and lower will work great. Qts is speakers total quality in Ratio to its electrical, and mechanical characteristics, Qms is the Mechanical ratio.
If you want to run a sub for more of a spl use, its better to run a woofer off of a Bass EQ/ Amp bass boost circuit/ Deck boost. But it cant be mixed frequecies, like a deck with a 60hz boost, and a amp with 40hz boost, you need to cancel 1 freq out, or level the 2 freq's (there will be cancelation, and the sub will sound like its being pushed to hard-boost for tline have to be close to the quarter wave of the box as possible) This allows you to use a shorter tline length, in comparison to the speakers natural Fs quarter wave length. But Tlines, with Low Q woofers, like .30 and lower, you will be amazed how low the subs will play, lower than the boxes quarter wave length- almost down to the next octave- Cleanly. So, your looking at about 20hz almost as loud as the subs 40hz peak tunning. (depending on cabin resonace of vehicle ofcourse)
So, enuff explained. Lets go over the math, because thats where people get stumped the most.... This box in the tutorial I made sunday, I kind of dont want to give away to much, the rest you guys need to learn first hand. And the camera ran out of batteries, and the sun was going down, I REALLY wanted to finish it before night fall. So SOME pics, towards the end are missing.
So, math--- Box is tuned to about 41hz. So... useing the formula up there^
6.89 feet long x's The combined cone area of these 2 12s, I needed to keep a Constant 160sq port, 6.89' long. This box is PB- 3/4" The customer isnt paying full amt for MDF- haha.. oh well, I braced it very well. Notice all the 45s, even seperateing the 2 woofers, that is to keep the air flowing Cleanly, so no turbulance effects sound, or spl, and again, Reinforces the box for strength. I even filled larger gaps with Bondo, and painted the inside with blue paint, to keep the box from absorbing to much moisture- I will resin it soon-where I can.
So, I started off with the wood cutting. I got all my basic cuts, then copied all the OD cuts with a router, so I dont screw up sealing joints later.

D94R · 03-10-2010, 03:49 PM

That post by forevrbumpn is what inspired me to go back to a Tline, he took the mystery out of it lol.

loganberry · 03-10-2010, 06:36 PM

lol hes a friend of mine, he can build some crazy subs and boxes for sure

D94R · 03-11-2010, 11:58 AM

I've modeled some some sub-down enclosures, and I'm not liking how much higher it makes the box sit(20+ inches). Center arm when down is right at 17" or so and I don't want to go much over that for comfort when resting my arm.

Logan, what's your take on having the port forward, or to the rear? Is it gonna make a huge difference? I may be sticking to one of my designs on the second page, maybe with slight tweaks to either.

loganberry · 03-11-2010, 10:50 PM

it depends where the sub is, sub forward port back box's only work good in crx's, if the sub is firing up, and port is forward or rear thats fine as long as there is at least 5-8 inches of clearence from rear port to back wall

D94R · 03-12-2010, 12:40 PM

Ah perfect, I'll be fine either way then as I'm going sub-up, but have different designs which have port forward or back.